The invention relates to a marine drive having two counter-rotating surface operating propellers.
The present invention arose during development efforts directed toward a marine drive enabling increased top end boat speed. This is achieved by raising the torpedo out of the water to reduce drag, and by using two counter-rotating surface operating propellers. Reducing torpedo drag by raising the torpedo above the surface of the water is known in the art, for example U.S. Pat. No. 4,871,334, column 3, lines 35+.
The present invention provides structure in the vertical portion of the drive permitting the noted raising of the torpedo without raising the transom mounting location for the drive.
In one aspect of the invention, an upper adaptor spool is provided at the top of the vertical bore of the drive unit and supports both the vertical driveshaft and the upper input gear.
In another aspect, structure is provided enabling assembly of the majority of the vertical drive train from above into the vertical bore of the drive housing.
In another aspect, the invention enables reduction of the vertical distance between the upper adaptor spool and the lower driveshaft bearing to be about equal to propeller radius.
In another aspect, the invention enables a onepiece unitary integrally cast housing, wherein in the preferred embodiment, the distance along the driveshaft between the lower concentric counter-rotating propeller shafts and the upper input shaft is in the range of about 9 to 15 inches.